1. Field of the Invention
The present invention relates generally to methods and apparatus for determining the volume of material milled or the area milled from a ground surface by a milling machine.
2. Description of the Prior Art
When working ground surfaces by means of milling machines, stabilizers or recyclers, and when mining deposits by means of mining machines (surface miners), the milled area and/or the milled volume is usually required as basis for the settlement of the services rendered for the purpose of documenting and settling the services rendered on the construction site. These data are determined or estimated, for example, from data previously known or determined from cartographic material or surveying documents, it being assumed here in a simplifying manner that the actually milled area or the actually milled volume precisely corresponds to the area to be milled or the volume to be milled that was previously stated in the contract.
It is also known to carry out, after completion of the milling operation, a more or less accurate determination of the milled area or the milled volume, respectively, by means of simple measuring instruments (for example, odometer and folding rule).
Lastly, it is also known to determine an approximated value of the currently milled volume and, by integration, establish a daily volume from the travelled distance, which can be read out from or is measured by a machine control system, and a milling depth, assuming that the milling drum width installed corresponds to the effectively milled milling width.
It has become apparent, however, that in practice the actually milled area or the actually milled volume deviates from the geometrical data stipulated in a service contract or from the data derived from surveying documents or maps with, as a general rule, the actually milled volume being the larger. This is therefore of disadvantage to the contracting company as the inaccurate settlement will be to its detriment. One reason for this may be, for example, the three-dimensionality of a course of, for example, a motorway section in a hilly area because the length of a milling trajectory is smaller in the map projection than in the three-dimensional course of the road. Another reason is additional work that was not known or not foreseeable prior to awarding the contract and is thus not reflected in the surveying documents or maps.
Measuring with simple measuring means (odometer, folding rule) is also merely a more or less accurate approximation to the actual service rendered as complex milling geometries are frequently also worked that are not accessible to calculation by way of simple means.
Such methods of settlement are not only inaccurate but also time-consuming.
More recently there has been proposed a system for automatically determining milled areas and/or milled volumes through the use of GPS or other technology to track the trajectory of the machine, and subsequent data-processing to add up milled areas or volumes and to subtract overlapping areas or volumes, as set forth in pending DE102011106139, also pending as PCT/EP2012/060505, the details of which are incorporated herein by reference.
There are, however, a number of difficulties encountered in the use of a GPS based system for tracking machine trajectories. One necessary condition for the use of GPS technology is a sufficiently large viewing angle in the sky. If the viewing angle is too small it will reduce the number of satellites that can be viewed and decrease the accuracy of the system. Also, so-called multi-path effects due for example to reflection of GPS signals off of tall buildings and trees can affect accuracy of the GPS system. As a result of such difficulties, a GPS based system may not be sufficiently accurate, especially in congested residential areas.
Accordingly, there is a continuing need for improved systems for the automatic determination of areas or volumes milled by such milling machines.